renderer: Pass event to behavior for processing

I6d9ff52b introduced a regression where if a logged out user clicks the
settings cog then an error is thrown.

For now, passing the event to the behavior for further processing is
required. However, it's clear that this makes the
ext.Popups.PreviewBehavior abstraction leaky.

Bug: T162324
Change-Id: I9dea04eb7435f9349e60d477f5701ec5dd655ebd

src/previewBehavior.js

@@ -2,6 +2,11 @@ var mw = window.mediaWiki,
 	$ = jQuery;
 
 /**
+ * A collection of event handlers specific to how the user interacts with all
+ * previews. The event handlers  are are agnostic to how/when they are bound
+ * //but not to what they are bound//, i.e. the showSettings event handler is
+ * written to be bound to either an `<a>` or `<button>` element.
+ *
  * @typedef {Object} ext.popups.PreviewBehavior
  * @property {String} settingsUrl
  * @property {Function} showSettings

src/renderer.js

@@ -280,7 +280,7 @@ function bindBehavior( preview, behavior ) {
 		.click( function ( event ) {
 			event.stopPropagation();
 
-			behavior.showSettings();
+			behavior.showSettings( event );
 		} );
 }